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Genomic Approach to Study the Role of Bacterioplankton in the Sulfur Cycle

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Bacteria and the sulphur cycle

The 'Genomic approach to study the role of bacterioplankton in the sulfur cycle' (GENS) project investigated how marine microorganisms metabolise the greenhouse gas dimethylsuflide (DMS) and its precursor dimethylsulfoniopropionate (DMSP). Genetic material recovered from environmental samples can help revolutionise our understanding of microbial energy sources.

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Scientists from the GENS project analysed the bacterial component of plankton to identify the genes involved in transforming DMSP to DMS. DMS released from ocean surface waters is the most important natural source of sulphur to the atmosphere, where it plays a key role in controlling the Earth’s climate through the formation of aerosols and cloud cover. Results showed that DMSP supports heterotrophic activity and depletes the transcriptome ( all RNA molecules) involved in light-related energy generation by the bacteria. Examination of gene expression patterns indicated that a wide range of bacteria used DMSP as a source of carbon and sulphur. Different communities of bacteria were sorted and sequenced. The work was conducted over two contrasting periods of the year and revealed two common life strategies found in the marine environment that - restricted and versatile with high DNA-low DNA flow cytometric signatures respectively. Researchers also studied the role of bacteria in the biogeochemical cycling of phosphorus and complementary energy sources. Microorganisms sampled from mountain lakes high up in the Pyrenees were compared with studies of marine microorganisms. Metatranscriptomics showed that these high-altitude lakes are significantly phosphorus-limited. The results revealed three main mechanisms employed by heterotrophic bacteria to take advantage of alternative energy from sunlight – one through oxidation of carbon monoxide. The other two involved photoheterotrophic mechanisms using pigments bacteriochlorophyll a and proteorhodopsin t. An improved understanding of the fate of DMSP in marine environments will not only provide greater insight into climate regulation and ocean–atmosphere interactions but also microbial food web dynamics and the biogeochemistry of carbon and sulphur.

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